Dumb Question

[lhdor]

I know I should know this, but please be kind.

What do the letter mean when you set the camera to 24p, 24pa, or 60i? I know what the numbers are, it's just the letters am a little confused.

[J.R. Hudson]

24 p(rogressive)
24 p(rogressive) a(dvanced) <<<<<<<<< Advanced Pulldown
60 i(nterlaced)


http://www.kenstone5.net/fcp_homepage/images_24p_in_FCP_nattress/32_pulldown.jpg

Advanced pulldown

Another pulldown pattern is the "advanced pulldown" ("24pA") pattern, first implemented in the Panasonic AG-DVX100 camcorder. Instead of padding the frames into a repeating 3:2 pattern, the frames are padded into a 2:3:3:2 pattern.

It converts the first frame into two fields, the second into three fields, the third into three fields, and the fourth into two fields. It then repeats this pattern for every group of four frames that follows. This pulldown pattern is used to avoid segmenting a 24p frame into two different 60i fields that exist in two different 60i frames. When a 24p frame is split up and recorded into separate 60i frames, interlacing artifacts can exist in the 60i frames. These artifacts decrease the compression efficiency of DV (http://en.wikipedia.org/wiki/DV) and can result in cycles of efficiency compression followed by less-efficient compression. The advanced pulldown scheme avoids this as every 24p frame can be found intact within the resulting sequence of 60i frames, yet the compression efficiency remains the same as with 3:2 pulldown.

When editing 24pA footage, conversion from 60i back to the original 24p is very efficient. It only requires blending the fields made from the frames back into full frames. Then, only every fifth frame will be made up of fields from two different frames, and that frame can be discarded, leaving only the other four full frames. In order for this to work properly, the editing system must know where the cadence pattern begins; that information is recorded with the footage and comes through with the data stream upon capture.

Because the 2:3:3:2 scheme was devised for efficient pulldown removal for editing, and because 24p editing applications more universally support its removal, it should always be used when planning to edit in native 24p.
Editing systems need specific support for the 24pA format to be able to detect and remove the pulldown properly so that the 24p frames can be edited in a 24p timeline. Many but not all prosumer and professional-level non-linear editing systems are able to recognize and remove this advanced pulldown scheme. However, among the editing applications able to remove pulldown and edit in native 24p, it is more common for them to have support for 24pA 2:3:3:2 pulldown than for standard 24p 3:2 pulldown removal.
Still other editing applications have the option for editing on a 24p timeline, and will accept footage where the pulldown has already been removed in another application.

Also because the 2:3:3:2 pulldown scheme was devised in order to make pulldown removal for editing in native 24p more efficient, the pulldown arrangement is not ideal for watching footage. There can be exaggerated stutters in motion, because the frames which are split into three fields are not only onscreen for 50% longer than the other frames, they are back-to-back. As such, 2:3:3:2 pulldown should be used only when a native 24p edit is planned, and not for final viewing. This includes when shooting the footage initially, and also when printing back to tape from an NLE.

[Dick Campbell]

Excellent discussion J.R. Thank you. So wjhat I take from this is that you want to use 24pA, if you intend to ultimately view in 60i? such as broadcast medium? Otherwise why not just shoot in 24pN?

[Luis Caffesse]

Actually no, if you intend to ONLY view in 60i, then you may as well shoot 24P and edit in a 29.97 timeline.

24PA is useful in that you can cleanly remove the pulldown and be left with a native 24fps file - to be edited in a 24fps timeline.

For example - when producing work for DVD or online distribution I tend to use 24PA (or PN on the HVX which records ONLY the 24 native frames with no duplicate frames). This leaves with me 24fps files which I edit in 24fps timelines and master as 24fps files.
When encoding these things for online or DVD, you can get a slightly higher bitrate due to the fact that you aren't taking up space encoding duplicate frames you don't need.

When I was working at a local TV stations here - I shot all the commercials using 24P, edited in a 29.97 timeline, and mastered at 29.97 - because that is what we broadcast in so there was no reason to ever bother with a native 24fps file.

I probably just confused you more....


***
OH - and to answer your other question - you can only shoot in PN mode when shooting 720.
So the 24PA setting is still very useful when shooting either 480 or 1080.

[lhdor]

Wow guys, thanks for clearing that up. I get it now and printed the discussion out so I won't forget.
I appreciate your help